Field of the Invention
This invention concerns an improved process for the reaction of carboxylic acids with vinyl ethers such as 3,4-dihydro-2H-pyran (dihydropyran) using monomeric and polymeric pyridine hydrochloride catalysts to produce acetal esters. The structure of the polymeric catalyst is a crosslinked poly 2-, 3-, or 4-vinylpyridine hydrochloride. The non-polymeric catalyst is a hydrochloride of pyridine or an alkyl-substituted pyridine with no more than one alkyl substituent in positions 2 and 6.
The prior art catalysts for the reaction of carboxylic acids with vinyl ethers to produce acetal esters have been strong acids such as sulfuric, hydrochloric and p-toluenesulfonic acid. The advantage of the monomeric and polymeric pyridine hydrochloride catalysts is that they are milder than the strong acids, allow better control of the reaction, and avoid the high corrosiveness of the stronger acids. The present invention is useful as a clean, commercially feasible method for synthesizing tetrahydropyranyl acrylate and methacrylate which are useful in photoresist and other applications.